foreach (@list)

##</code><code>##

while (<>)

##</code><code>##

push @{ $ipURL{$ip} }, $url;

##</code><code>##

my ($ip, $url) = (split /,/)[7, 31];

##</code><code>##

perl -wE 'for (1..10000) {say join ",", map int rand 1000, 1..35}' > input

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

open my $FH, '<', 'input' or die $!;

sub slow {
    my ($fh) = @_;
    seek $fh, 0, 0;
    my @list = <$fh>;
    my $linecounter;
    my %ipURL;
    foreach (@list) {
        $linecounter++;
        my @message=split(',',$_);
        my $ip=$message[7];
        my $url=$message[31];

        if (!(exists $ipURL{$ip})) {
            my @urlList;
            push(@urlList,$url);
            $ipURL{$ip}= \@urlList;
        } else {
            my @urlList=@{$ipURL{$ip}};
            push (@urlList,$url);
            $ipURL{$ip}=\@urlList;
        }
        if (!($linecounter % 50000)) {
                print "Lines: $linecounter\n";
        }
    }
    return \%ipURL
}

sub fast {
    my ($fh) = @_;
    my %ipURL;
    seek $fh, 0, 0;
    while (<$fh>) {
        my ($ip, $url) = (split /,/)[7, 31];
        push @{ $ipURL{$ip} }, $url;
    }
    return \%ipURL
}

use Test::More tests => 1;
is_deeply slow($FH), fast($FH), 'same';

use Benchmark qw{ cmpthese };
cmpthese(-3, {
    slow => sub { slow($FH) },
    fast => sub { fast($FH) },
});

##</code><code>##

1..1
ok 1 - same
       Rate slow fast
slow 20.7/s   -- -26%
fast 27.9/s  35%   --